The present invention relates to a sense amplifier used, for example, in a static-type semiconductor memory device, one of the functions of the sense amplifier being to select one of a plurality of input signals.
In a static-type RAM device, a very small voltage difference of, for example, about 0.5 V, output from a memory cell and transmitted to a pair of data buses, is amplified by a sense amplifier when readout operation is effected.
However, in a conventional static-type RAM device, especially a large capacity RAM device, since a bit line pair, column transfer gates, and a data bus pair are connected to a selected memory cell, the load of the memory cell becomes heavy, and the readout speed is deteriorated. Especially, in a large capacity RAM device, each bit line and data bus become long and thin, and the on-resistance of the column transfer gates becomes large. Therefore, if the driveability of each memory cell is not large, it takes a long time for the input signal of the sense amplifier to reach a steady state signal level.